Agitation blade

ABSTRACT

A stirring blade unit includes a perforated cylinder formed around the an internal stirring blade so as to be rotated together with the stirring shaft. The perforated cylinder has perforations which are approximately 30 to 50% of the area of the top and bottom surface of the perforated cylinder. The internal stirring blade unit uses a discharge type stirring blade unit used for gas-liquid mixing of a general fermentation tank. Thus, the gas-liquid flow discharged from the blade unit in the horizontal direction hits the perforated cylinder formed around the blade unit certainly. Due to this hitting of the gas-liquid flow against the perforated cylinder, the pressure of the flow is changed significantly to refine the gas bubbles so that the gas absorption property is improved. The stirring blade unit is suitable for gas-liquid mixing necessary for such as, fermentation, aeration, and reaction (hydrogenation and oxidation) tanks. The gas-liquid mixing blade unit can absorbs gas efficiently and thus, reduces both the manufacturing cost and installation space.

This application is a 371 of PCT/JP98/00106, filed on Jan. 14, 1998.

FIELD OF THE INVENTION

The present invention relates to stirring blade units, more particularlyto a stirring blade unit that, used in a gas-liquid mixing tank, refinesand disperses a gas supplied from a nozzle or a sparger provided justunder said blade unit into a liquid to absorb said gas at a low cost, ina compact space, and at a high efficiency.

BACKGROUND OF THE INVENTION

Gas-liquid mixing is adopted in various processes, typically infermentation, waste water treatment, oxidation, hydrogenation, etc.Among those processes, aeration stirring can satisfy the required volumeof oxygen for culturing in an aerobic fermentation process due to theaeration and stirring functions, but actually, in many cases ofgas-liquid mixing, the productivity is decided by the oxygen supplycapacity of the fermentation tank in use. The main object of thegas-liquid mixing will be to refine and disperse bubbles and absorb gascomponents into a liquid. As for gas absorption in a gas-liquid contactmaker using a stirring tank, a well known relational expression (seeIndustrial Engineering Chemistry, volume 45, page 2554-2560 (1944)) is,as follows:

Kla∝Pv ^(α) ×Us ^(β),

wherein

KL is the mass transfer coefficient of liquid stirring;

a is the gas-liquid interface are per unit volume;

Pv is the stirring power per unit volume;

Us is the superficial gas velocity; and

α, β are constants.

In order to improve the efficiency of gas absorption, a problem of howto increase the gas-liquid interface area a, that is, how to minimizebubbles in size and disperse them, must be solved. Because, the KL inthe above expression is decided by the solid state properties and fluidstate of the material. Actually, however, the stirring power Pv andaeration capacity Us are increased to solve the problem.

In addition, in order to achieve the above object, measures had to betaken to refine bubbles efficiently while both stirring power andaeration capacity were suppressed from increasing as much as possible,as well as a more effective stirring blade unit had to be developed.And, in recent years, there are introduced a blade unit that can mix gasand liquid efficiently without damaging the microorganisms (UnexaminedPublished Japanese Patent Application No. 5-103956), a fermentation tankimproving method that can improve the ferment shift capacity coefficient(KLa) by fixing a wire mesh in the target fermentation tank so as tosurround the stirring blade unit(Examined Published Japanese PatentApplication No. 3-4196), an effective method of mixing and gas-liquidcontact by providing a gas inlet at the tip of the stirring blade unit(Examined Published Japanese Patent Application No. 57-60892), astirring blade unit that can improve the stirring mixture effectivelyusing a stirring blade unit that can rotate a pair of propellers and aperforated cylinder together (Unexamined Published Japanese PatentApplication No. 6-85862), etc. and their effects are already confirmed.

Actually, however, it will be difficult to improve gas absorption byincreasing the above stirring power and aeration capacity. Because theincrease of those items is accompanied by expansion of the equipment andincreasing of energy. When increasing the stirring power, measures suchas increasing the rotation speed of stirring and increasing the bladesize are thought of, but those measures will require improvement andreinforcement of some components related to the stirring, such asmodification of the agitator itself, increasing of the strength of thestirring tank, etc. Especially, it will be difficult to apply such theimprovement and reinforcement as mentioned above to existing equipmentfor the reasons of construction method and cost in many cases.

Furthermore, when operating any of those developed in recent years in anindustrial scale, it will arise problems that the rotation speed must bemore increased to obtain the expected effect, the equipment will becomemore complicated in structure, and the equipment will be more expandedin size (so that it cannot be fixed in the target stirring tank), etc.When the power characteristics of the blade unit differ from those ofthe conventional blade unit such as turbine blades, etc., the bladeswill be more expanded in size. In such a case, therefore, it will bedifficult to apply the blade unit to any of existing stirring equipment.

DISCLOSURE OF THE INVENTION

Under such the circumstances, it is an object of the present inventionto solve the above prior art problems and provide a compact stirringblade unit that can absorb a gas more efficiently and be used in agas-liquid mixing tank.

In order to achieve the above object, the present invention provides adischarge type stirring blade unit, in which a perforated cylinder isformed around the stirring blade unit so as to be rotated together withthe shaft of the stirring blade unit. The numerical aperture of theperforated cylinder rotated together with the shaft in the presentinvention should be 30 to 50%.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a and 1 b are a top plan view and side elevational view,respectively, of the entire stirring blade unit 5 of the presentinvention (when a cylindrical blade unit is used as the internalstirring blade unit), wherein the side elevational view has portions ofthe outer perforated cylinder 2 removed for clarity of view of theinternal stirring blade unit 1.

FIG. 2 is a cross-sectional view showing the use of the entire stirringblade unit 5 of the present invention, shown in FIGS. 1(a) and 1(b), ina stirring tank 9 in the first example.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereunder, the examples of the present invention will be described withreference to the attached drawings.

FIGS. 1(a) and 1(b) are a top plan view and a front view, respectively,of the entire stirring blade unit 5 in an example of the presentinvention. The basic structure of the entire stirring blade unit 5 ofthe present invention is characterized by a perforated cylinder 2 formedaround a discharge type internal stirring blade unit 1 provided with adisc 8 preventing bubbles from going up, i.e., the internal stirringblade unit 1 being defined as being made up of the disc 8 and the blades3, while the entire stirring blade unit 5 includes the perforatedcylinder 2, the shaft 4, and the internal stirring blade unit 1. Theperforated cylinder 2 is rotated together with the shaft 4 of theinternal stirring blade unit 1. In FIGS. 1(a) and 1(b), the internalstirring blade unit 1 is formed as a cylinder blade unit havingcylindrically-shaped blades 3. The internal stirring blade unit 1 isgenerally a discharge type stirring blade unit and is used forgas-liquid mixing for a fermentation tank, etc. The entire stirringblade unit 5 is structured so that the gas-liquid flow, discharged bythe internal stirring blade unit 1 in the horizontal direction, hits theperforated cylinder 2 formed around the internal stirring blade unit 1certainly. When a discharge type stirring blade unit is used as theinternal stirring blade unit 1, the gas-liquid flow discharged from theinternal stirring blade unit 1 can hit the perforated cylinder 2vertically to change the pressure of the flow significantly. In thepresent invention, therefore, a discharge type stirring blade unit isused. It is not an axial flow type one. Because of the pressure changecaused when the gas-liquid flow hits the perforated cylinder 2, gasbubbles are refined and absorbed more rapidly. In addition, since theperforated cylinder 2 is rotated together with the shaft, the perforatedcylinder 2 can be formed very closely at the tip of the internalstirring blade unit 1 where the discharged gas flows most strongly toobtain the maximum pressure change. If the perforated cylinder 2 isfixed in the stirring tank 9, a clearance must be formed between theinternal stirring blade unit 1 and the perforated cylinder 2 in order toprevent impact between them. Thus, the maximum pressure change will notbe obtained and the efficiency of the gas absorption will be lowered.

The internal stirring blade unit 1 of the present invention may be aflat turbine blade unit, a pitched turbine blade unit, a concave bladeunit, a cylindrical blade unit, etc., if it is a discharge type one.

The perforated cylinder 2 used for the entire stirring blade unit 5 ofthe present invention should have a numerical aperture of 35 to 45%,i.e., perforations P make up 35 to 45% of the area of the sidewall ofthe perforated cylinder. The structure should be a punched metal or meshcylindrical body. The height L and diameter r of the perforated cylinder2 should be 1.5 to 3 times the width b of the blade 3 of the internalstirring blade unit 1 and 1.01 to 1.05 times the diameter of theinternal stirring blade unit 1. The material of the perforated cylinder2 may be ceramic, stainless steel, iron, etc. if it has enough strengthfor use.

The internal stirring blade unit 1 and the perforated cylinder 2 can beattached, as follows: the perforated cylinder 2 is welded or bolted tothe tip of the internal stirring blade unit 1 or the lug of theperforated cylinder 2 is attached to the disc 8 of the internal stirringblade unit 1 to fix the perforated cylinder 2, for example. In addition,the perforated cylinder 2 should be positioned so that the blade 3 ofthe internal stirring blade unit 1 comes into the center of theperforated cylinder 2.

Furthermore, in the present invention, such a gas as air may beventilated by a single-hole nozzle, a multi-hole nozzle, a sparger,etc., any of which are represented by reference numeral 6, provided justunder the entire stirring blade unit 5 of the present invention. Theaeration method is not limited specially.

Thus, the entire stirring blade unit 5 of the present invention canrefine bubbles more and accordingly, improve the gas absorptionefficiency in a gas-liquid mixing tank (for hydrogenation, etc.) morethan the prior art stirring blade units.

EXAMPLES

Hereunder, the present invention will be explained in more detail belowwith reference to the examples, i.e., Example 1, Example 2, and UsageExample 1.

Example 1

The first example of the present invention will be explained withreference to FIG. 2.

FIG. 2 is a cross-sectional view of the entire stirring blade unit 5used for a measurement. The stirring tank 9 is a cylindrical stirringtank provided with a 70 L transparent acrylic lid. The bottom of thetank 9 is mirror-processed (10% end shape). In addition, eight 30-mmwide baffles 7 are attached symmetrically on the wall of the tank. Theliquid depth HL is decided as HL/D=1 (D=400 mm) to the diameter of thetank 9. Then, the effect of the present invention was checked bymeasuring the oxygen transfer rate OTR (generic name of oxygen transferrate: OTR ∝Kla) of the entire stirring blade unit 5 in the abovestirring tank 9 using the sulfite oxidation method. The entire stirringblade unit 5 of the present invention was put just above the spargernozzle 6 provided near the bottom of the tank 9 and a gas was suppliedfrom the nozzle 6 as a rate of 0.85 VVM (gas volume/charge liquid volumeper min) for the above measurement. In this case, 8-turbine blades andcylindrical blades 3 (diameter d=110 mm, width b=21 mm of each blade 3commonly) are used for the internal blade unit 1 of the presentinvention. As the perforated cylinder 2, a punched metal (diameter r=115mm, height h=50 mm, numerical aperture=38%, hole diameter=2 mm) wasused. As shown in Table 1, when the entire stirring blade unit 5 of thepresent invention was used, the oxygen transfer rate OTR was improved by26% in maximum at the same stirring power (Pv=1 kW/m³) when comparedwith the prior art 8-turbine-blade unit used generally for gas-liquidmixing or the “EGSTAR” (product name of EBLE (Inc.)). The8-turbine-blade unit used in this test was a stirring blade one (bladediameter d=110 mm, width b=21 mm, cylinder height L=200 mm) comprising apair of propeller blades and a perforated cylinder that were rotatedtogether to improve the efficiency of stirring mixture (described inExamined Published Japanese Patent Application No. 6-85862).

TABLE 1 Comparison of Oxygen Transfer Rates among Stirring Blade UnitsOxygen Transfer Rate OTR Difference Stirring Blade Unit OTR [mol/m³ ·hr] [−] 8-turbine-blade unit 116.4 1 “EGSTAR” 87.5 0.75 Presentinvention 130.9 1.13 internal blade unit: 8-turbine-blade unit Presentinvention 146.9 1.26 internal blade unit: Cylindrical blade unit *TheOTR difference indicates the value of each stirring blade unit when the8-turbine-blade unit OTR is assumed to be 1.

Then, the oxygen transfer rate OTR change was measured by changing thenumerical aperture of the perforated cylinder used in the stirring bladeunit of the present invention explained above under the same conditionsas the above. Table 2 shows measurement results when the numericalaperture of the perforated cylinder is changed to 0, 30, 35, 44, 50, and55% respectively. The OTR value in Table 2 is a value when the stirringpower is 1 kW/m³ . When the numerical aperture is 30 to 50% in Table 2,it is found that the oxygen transfer rate is higher than that of the8-turbine-blade unit. When the numerical aperture is larger, thedischarge flow passes through the perforated cylinder more easily. So,the pressure change to be generated both inside and outside theperforated cylinder becomes smaller. In addition, when the numericalaperture is smaller, the resistance of the flow becomes largeexcessively due to the function of the perforated cylinder. Thus, thedischarge flow cannot pass through the perforated cylinder.

TABLE 2 Difference of Oxygen Transfer Rate OTR by Numerical ApertureChange Numerical Oxygen Transfer Stirring Blade Aperture Rate OTR OTRDifference Unit [%] [mol/m³ · hr] [−] 8-turbine-blade — 116.4 1 unitPresent 0 97.5 0.84 inventions 30 117.2 1.01 internal 35 146.9 1.26stirring blade 44 132.5 1.14 unit: Cylindrical 50 122.4 1.05 blade unit55 115.3 0.99 *The OTR difference indicates the value of each stirringblade unit when the 8-turbine-blade unit OTR is assumed to be 1.

Example 2

The stirring blade unit of the present invention was attached in a 2.5m³ fermentation tank and the oxygen transfer rate OTR was measured usingthe sulfite oxidation method. The stirring conditions were as follows;the liquid volume was 1.5 m³, the aeration volume was ⅓ VVM, thetemperature was 30 C. The sparger nozzle provided just under thestirring blade unit was used for aeration just like in the firstembodiment. In this case, a cylindrical blade unit (blade diameter d=500mm, width b=80 mm) was used as the internal stirring blade unit and apunching metal (diameter r=510 mm, height h=190 mm, numericalaperture=40%, and hole diameter=5 mm) was used as the perforatedcylinder. In a comparison test, an 8-turbine-blade unit (blade diameterd=500 mm, width b=80 mm) was used instead of the stirring blade one ofthe present invention. The test conditions were the same as those of theabove test.

As a result of the measurement performed under the above conditions, theoxygen transfer rate OTR was improved by about 25% to 107.7 mol/m³,although it was 86.4 mol/m³.hr for the 8-turbine blade unit under astirring power of 1 kW/m³.

Usage Example 1

The stirring blade unit of the present invention was attached in a 2.5m³ fermentation tank and L-glutamic acid was fermented as follows usingbrevibacterium flavum QBS-4 FERM P-2308 described in Examined PublishedJapanese patent Application No.52-024593.

At first, the culture medium comprising the components as shown in Table3 was adjusted and it was transferred into a 500 ml flask in units of 20ml and heated at 115° C. for 10 min for sterilization. Then, it wasseed-cultured.

TABLE 3 Seed Culture Medium Component Concentration Glucose 50 g/l Urea4 g/l KH₂PO₄ 1 g/l MgSO₄ · 7H₂O 0.4 g/l FeSO₄ · 7H₂O 10 g/l MnSO₄ · 4H₂O10 g/l Thiamine hydrochloride 200 g/l Biotin 30 g/l Soybean proteinhydrolytic substance 0.9 g/l (as the whole ferment volume)  (pH 7.0)

Subsequently, the main culture medium shown in Table 4 was adjusted andsterilized at 115 C. for 10 min. After this, a seed culture mediumliquid was inoculated and main-cultured at 31.5 C. in a 2.5 m³fermentation tank. In this case, the stirring conditions were asfollows; the rotation speed was 175 rpm and the aeration volume was ½VVM. For the aeration, a sparger nozzle provided just under the stirringblade unit was used just like in the example 1. As the stirring bladeunit for culturing, an 8-turbine-blde unit (blade diameter d=500 mm,width b=80 mm) and the stirring blade unit of the present invention wereused for culturing respectively. As the internal stirring blade unit ofthe present invention, a cylindrical blade unit (blade diameter d=500mm, width b=80 mm) was used. As the perforated cylinder, a punchingmetal (diameter r=510 mm, height h=190 mm, numerical aperture=40%, holediameter=5 mm) was used. During the culturing culture medium pH wasadjusted to 7.8 with an ammonia gas. When the succharum in the culturingliquid was consumed up, the fermentation was ended and the L-glutamicacid accumulated in the culturing liquid was measured. Table 5 shows theculturing result.

As a result, when the stirring blade unit of the present invention wasused, the oxygen transfer rate was improved, so that the L-glutamineacid generation rate was improved by about 25% to 3.14 g/l/hr from 2.51g/l/hr as shown in Table 5.

TABLE 4 Main Culture Medium Component Concentration Waste syrup (asglucose) 150 g/l KH₂PO₄ 1 g/l MgSO₄ · 7H₂O 1 g/l Thiamine hydrochloride100 g/l Anti-foaming agent 20 μl/l  (pH 7.0)

TABLE 5 Culturing Result L-glutamic acid L-glutamic acid accumulatedvolume generation speed Stirring Blade Unit (g/l) (g/l/hr)8-turbine-blade unit 75.2 2.51 Present invention’s 76.1 3.14 blade unit

Industrial Applicability

The discharge type stirring blade unit of the present invention ischaracterized by a perforated cylinder rotated together with thestirring shaft around the blade unit and having a numerical aperture of30 to 50%. The blade unit thus allows the gas-liquid flow dischargedfrom the blade unit to hit the perforated cylinder, changing thepressure of the gas-liquid flow significantly. As a result, the gasbubbles can be refined efficiently to improve the efficiency of gasabsorption in the gas-liquid mixing tank, as well as improve theenergy-saving effect.

Furthermore, when improving an existing stirring tank that uses adischarge type blade unit such as a turbine blade one, it is only neededto replace the stirring blade unit with the blade unit of the presentinvention to improve the performance. No other significant modificationsuch as replacement of the motor and reducer, reinforcement of thefermentation tank is required. Because, the power characteristics arenot different so much between the existing blade unit and the blade unitof the present invention.

The stirring blade unit of the present invention will be useful for afermentation tank, an aeration tank, a reaction tank (hydrogenation andoxidation), etc.

What is claimed is:
 1. A stirring blade unit comprising: a rotatableshaft; a disc for preventing gas bubbles from going up through a top ofsaid stirring blade unit, wherein said disc is fixedly attached to androtates with said rotatable shaft; a plurality of blades for gas-liquidmixing, wherein each of said plurality of blades has a first end whichis fixedly attached to said disc at an end of said disc which isopposite of where said disc is fixedly attached to said rotatable shaft;a perforated cylinder rotating together with said rotatable shaft by wayof said perforated cylinder being formed around said plurality of bladesattached to said disc and a second end of each of said plurality ofblades being fixedly attached to an inner surface of a sidewall of saidperforated cylinder at an approximately central portion of saidperforated cylinder, wherein said perforated cylinder has perforationsin said sidewall thereof, said perforations making up approximately 30to 50% of an area of said sidewall of said perforated cylinder.
 2. Thestirring blade unit according to claim 1, wherein each of said pluralityof blades is selected from a group consisting of a flat turbine blade, apitched turbine blade, a concave blade, and a cylindrical blade.
 3. Thestirring blade unit according to claim 1, wherein said perforatedcylinder comprises a body selected from a group consisting of a punchedmetal cylindrical body and a mesh cylindrical body.
 4. The stirringblade unit according to claim 1, wherein said perforated cylinder has aheight, which is 1.5 to 3 times a width of each of said plurality ofblades, and an outer diameter, which is 1.01 to 1.05 times a diametermeasured from a tip of a first blade of said plurality of blades to atip of a second blade of said plurality of blades where said first bladeand said second blade are each attached to said disc so as tosymmetrically oppose each other across a diameter of said disc.
 5. Astirring blade unit comprising: a discharge-type blade for gas-liquidmixing; a stirring shaft on which said discharge-type blade is mounted;and a perforated cylinder rotating together with said stirring shaft,wherein said perforated cylinder is attached to said discharge typeblade, wherein said perforated cylinder is open at a top and bottomthereof, and wherein said perforated cylinder has perforations in asidewall thereof so that said perforations make up approximately 30 to50% of an area of said sidewall of said perforated cylinder.
 6. Thestirring blade unit according to claim 5, wherein said discharge-typeblade is selected from a group consisting of a flat turbine blade, apitched turbine blade, a concave blade, and a cylindrical blade.
 7. Thestirring blade unit according to claim 5, wherein said perforatedcylinder comprises a body selected from a group consisting of a punchedmetal cylindrical body and a mesh cylindrical body.
 8. The stirringblade unit according to claim 5, wherein said perforated cylinder has aheight which is 1.5 to 3 times a width of said discharge-type blade anda diameter which is 1.01 to 1.05 times a diameter of said discharge-typeblade.